Wimbledon champion Petra Kvitova became the latest casualty of an unpredictable women’s US Open last night when she was shocked 6-4, 6-4 by unknown Serb Aleksandra Kunic.

The third seed joined No 2 Simona Halep on the scrapheap after losing to the 21-year-old qualifier — who has never even played in the main draw of a Grand Slam before.

Standing just 5ft4in tall, Krunic took advantage of numerous errors in the strong breeze from the below-par Kvitova, who was unrecognisable as the player who put on such a stunning display in the final at SW19 less than two months ago.

Despondent: The world number four Petra Kvitova crashed out of the US Open in the third round

Shock: Serbian qualifier Aleksandra Krunic beat Kvitova 6-4 6-4 as the top seeds continue to exit the US Open

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Kvitova became the fifth of the top 10 seeds to fall, although Serena Williams, Maria Sharapova and Eugenie Bouchard survive.

Caroline Wozniacki continued to bounce back from her split with golfer Rory McIlroy as she reached the fourth round with a strong 6-3, 6-2 win over 18th seed Andrea Petkovic.

But she now faces a severe challenge against Sharapova, who was at her dogged best in defusing the power of former Wimbledon finalist Sabine Lisicki. She won 6-2, 6-4 in a game that finished well after midnight.

Bright future: Krunic had never won a grand slam match before the US Open and is ranked at 145 in the world

Trouble: Petra Kvitova loses early again at the US Open, having never been beyond the fourth round in New York

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